1. Field of the Invention
The invention relates to air filters and, more particularly, to an improved pleated filter media for high velocity air filters.
2. Summary of Related Art
Air filters are well known devices wherein air is drawn or forced into a housing and caused to pass through a filter unit having a full flow, pleated filter media to remove the dirt, dust particles and other contaminants carried in the air. Substantially clean air is thereby passed to the point of usage, such as an internal combustion engine.
Such air filters generally comprise a filter housing provided with an air inlet and an air outlet. A filter element is mounted within the housing and is interposed between the inlet and outlet of the housing. A seal is positioned to seal the inlet from the outlet so that no air can pass out of the outlet without having first passed through the filter element. The filter element is conventionally constructed of a pleated paper type filtering material folded in a manner to define a series of circumferentially arranged and axially extending pleats. The filter element is generally cylindrically-shaped, and may be frustoconically-shaped.
High velocity air filters have heretofore included pleated paper filter elements in which the length of all of the pleats is the same; that is, the distance from the radially outer edge of a pleat to the radially inner edge of a pleat is substantially the same for all of the pleats. However, in applications requiring relatively compact air filters, the inner diameter of the filter element is reduced to the point that the inner, or downstream, edges of the pleats tend to become unduly crowded. This causes increased restriction of air flow through the filter element, resulting in a loss of engine power.
Filter elements for relatively low velocity oil filters have been provided with long pleats alternating with much shorter pleats, often referred to as a "W" or "M" pleat configuration, for many years. The purpose of the "W" or "M" pleat configuration in oil filters is to increase the total surface area of the filter media employed in the oil filter element. A staggered short pleat configuration has heretofore never been utilized in a filter element for a high velocity air filter application, nor would the "W" or "M" pleat configuration as used in oil filters be suitable in a high velocity air filter. In addition, with the "W" or "M" pleat configuration as used in oil filters, independent spacer formations are generally required to evenly space each pleat from the adjacent pleats.